The major emphasis of this research program will focus on studies of the ocular physiology of the teleost. Results have indicated that carbonic anhydrase is an essential component of the countercurrent oxygen multiplier which is associated with the rete mirabile found in the teleost choroid. An anatomical description of these vessels will be given and the histochemical localization of carbonic anhydrase within them will be determined and correlated with our hypothesis of countercurrent oxygen multiplication. The influence of hyperbaric oxygen tensions on teleosts and other vertebrate retinas will be investigated. Studies have indicated that the teleost retina is resistant to oxygen toxicity, whereas frog retinas are not. The influence of hyperbaric oxygen on Na-K-Mg ATPase will also be investigated. We hypothesize that a major component of oxygen toxicity is mediated through inactivation of the Na-K-Mg ATPase while resistance to oxygen toxicity is brought about by the enzyme superoxide dismutase. Separation and qualitative identification of the enzyme will be attempted after a suitable assay procedure is developed.